The invention relates to a method and apparatus for detecting broken reinforcement cords in a tire sidewall.
When a tire goes flat, is run long periods of time underinflated or hits road objects, the reinforcement cords in the carcass ply are sometimes broken without any visible change in the tire. When the cords are broken, however, eventually there is a separation that manifests itself in what is called a zipper break (because it looks like an open zipper) in the sidewall.
Unseen cord breaks are particularly a problem when retreading tires, because the expense and time needed to retread a defective carcass is wasted.
Although some experienced individuals have acquired the ability to recognize such sidewall defects with good precision on observation, such individuals are scarce, and it is important that a correct diagnosis be made each time a tire carcass is inspected prior to retreading.
X-ray inspection has been used in retreading operations, but x-ray equipment is expensive, requires extra safety precautions to use, and some breaks, where the broken ends are not displaced, may not be observable on the x-ray screen.
Commercial ultrasonic units are believed to be used by Bandag in retreading operations.
It is an object of the present invention to provide a reliable, inexpensive method of detecting cord breaks in the carcass of a pneumatic tire, and to provide an apparatus to be used in the method. Other objects of the invention will be apparent from the following description and claims.